1. Field of the Invention
This invention pertains broadly to cable storage and dispensing (payout) systems. In greater particularity, the invention relates to a fiber pack that can be rapidly and easily assembled and that can be rapidly paid out with minimal fiber trauma.
2. Description of the Related Art
Deployment, otherwise known as payout, of long length cables (5 kilometers or more) can be performed in a variety of ways. One of the simplest ways is to wind the cable around a cylindrical spool, place a rod through the center of the spool and then pull the cable from the outside of the spool as the spool is rotated around the rod, For long lengths of cable, the large inertial forces of the cable pack will require a substantial power source to rotate the cable spool during cable deployment. Because of these inertial forces, quick starts and stops of the deployment process are difficult. Another disadvantage inherent in this method is that access is not allowed to both ends of the cable during payout. If the inside (radially inward) end of the wound cable were fixed in relation to spool rotation, the rotations of the spool during payout will result in axial twists of the cable. An accumulation of these twists will eventually result in cable damage. In many cases it is desirous that the inside end of a cable pack be fixed to permit the transmission of electrical or optical signals during deployment. Optical slip rings have been devised to accomplish this but these are extremely expensive.
Another outside cable payout method is a passive payout technique. In this method cable is pulled from a stationary spool in a direction that is coaxial with the spool's axis. Sewing machine bobbins use this common payout scheme. This method, like the first discussed, introduces an axial twist into the cable each time a wrap of cable is unwound from the cable spool. As previously stated, an accumulation of these twists can cause damage to the cable, particularly if the cable is reused.
For both rotating (active) and stationary (passive) spool techniques, the axial twists that occur to the cable during deployment can be nullified by introducing one counter-rotated twist in the cable for each wind of cable around its spool.
Several limitations and disadvantages are present with these outside payout techniques. For rapid payout, fiber height is generally limited to approximately 4.5 inches from the spool's core to the spool's flange. It was found that during payout, dispensed cable will not climb any higher distances in a reliable fashion. Thus, to increase the capacity of these spool arrangements, either the axial length of the spool or both of the core and flange diameters would need to be increased, while maintaining the maximum core-to-flange height. Such spools would be undesirably large in size.
Further increasing the size of these outside cable payout designs is their payout shrouds. A shroud or hood reduces the cable helix formed during high speed payout, keeping the dispensed cable in line with the spool's axis. The shroud also prevents the cable's helix from snagging on external hardware.
Another characteristic inherent with the passive outside payout techniques is the substantial payout tension required to dispense the cable. This tension typically runs anywhere from one to five pounds.
A third method of dispensing cable is with an active outside payout mechanism. In this method a mechanized arm is used to unwind cable from the utilized spool. One such active cable handling method uses a mechanism to maintain a constant cable payout tension. In this method the mechanized arm rotates around the cable spool and actively unwinds cable from the spool when cable payout tension is high and winds cable back onto the spool when cable payout tension is low. This wind/unwind action produces an automatic payout and pickup device for cable handling. Disadvantages of this system include mechanical complexity (increasing chance for failure); the requirement for an active drive mechanism to dispense cable; fixed cable length; and difficult cable replacement.
Inside payout is a cable payout dispensing method similar to the passive outside payout method. Cable is dispensed axially from a cable pack, starting from the inside of the cable pack and working outwardly. As with the outside payout method, cable preparation requires that a single axial twist be applied for every turn of the cable onto the utilized spool. Previous experience has dictated that the cable must be precision wound to improve packing efficiency and that an adhesive be applied to each layer of cable to keep the cable pack from falling inward into the hollow center of the pack. This combination of precision winding and adhesives has been thought to be necessary to maintain cable pack stability; however, preparing the cable pack in this fashion has proven to be a very tedious process, taking up to one hour to wind a single kilometer of cable.
After the cable is wound using the above described technique, it is placed in a container and is foamed in place. The hardened foamed packaging provides further support to keep the cable pack intact after the spool's inner core is removed. Removal of this foam is not a simple task and if not properly done, the foam can break into a multitude of minute non-biodegradable pieces that pose a possible pollution hazard.
The advantages of an inside payout cable pack include the ability to store long cable lengths in a compact profile and to dispense cable at small payout tensions (less than one pound). However, disadvantages of this scheme include the excessive time required to prepare cable packs for payout, the complexity of equipment to precision wind and foam the cable packs, and the accumulation of adhesives on the cable's outer jacket.
There is thus the need to provide a compact, reliable, easily prepared and reusable method for dispensing long lengths of cable.